Proposal for the 'long long' problems

[Phil Edwards <pedwards at disaster dot jaj dot com>]

After much grepping, methinks that all of the uses of _GLIBCPP_USE_LONG_LONG
guarding fall into three categories:

 1)  I/O
     This includes the various put, get, do_* functions.  They depend on
     C99 functions like strtoll and strtoull.

 2)  Math
     Specializations for numeric_limits, additional functions like div/lldiv
     and abs/llabs, additional lldiv_t declaration if needed.

 3)  <witty name goes here>
     General support in the form of additional specializations for
     _Is_integer, __is_integer, type_traits, and concept checking.  No
     telling who/what are using these, so if 'long long' is on, these should
     be present.

I propose:

a)  Because the default is now to enable them, the help text for
    GLIBCPP_ENABLE_LONG_LONG should be changed to say that --disable-long-long
    is that one that needs to be explicitly used, not --enable.  A 1-line diff.

b)  Same for GLIBCPP_ENABLE_C99.

c)  The ac_c99_* variables be more granular.  For example, if lldiv_t is not
    available, we turn off ac_c99_stdlib, which may have been turned on by the
    presence of strtoll & company.  Granted that the {presence,absence} of one
    probably indicates that of the other, we can't tell from the result.

d)  Instead of one preproc symbol, we define three:
    _GLIBCPP_USE_LONG_LONG_IO     if strtoll, etc, are present; predicate
                                  this on (the reworked) ac_c99_stdlib and
                                  maybe ac_c99_wchar
    _GLIBCPP_USE_LONG_LONG_MATH   if lldiv_t and such are present; predicate
                                  on ac_c99_math (including lldiv_t)
    _GLIBCPP_USE_LONG_LONG_ANY    if any 'long long' support is possible
                                  anywhere at all

Finally,

e)  We replace the generic USE_LONG_LONG by the more specific guards:  case
    (1) with _IO, (2) with _MATH, and (3) with _ANY.

Actually, I would argue that the constructs currently guarded in (3) should
not be guarded at all.  They only depend on the compiler understanding a
type 'long long'.  They don't need any of the C99 features being examined.


Phil

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